1. Field of the Invention
The present invention relates to high voltage transformers for
microwave ovens and manufacturing methods therefor, and more particularly, to an improved high voltage transformer for a microwave oven including a core, and primary and secondary coils, and an improved manufacturing method therefor.
2. Description of the Related Art
A typical microwave oven comprises a casing or housing having a cooking chamber and an electronic component compartment, a door for the cooking chamber, and a control panel installed in front of the electronic component compartment. A plurality of electronic components are housed in the electronic component compartment. These electronic components include a high voltage transformer for generating high voltage when the microwave oven is supplied with power from a power supply, a high voltage capacitor which is charged to a high voltage by the high voltage transformer, and a magnetron for generating microwaves and radiating the microwaves into the cooking chamber when discharge of the high voltage capacitor supplies the magnetron with high voltage.
FIG. 8 is an exploded perspective view of a conventional high voltage transformer, while FIG. 9 is an enlarged cross sectional view taken generally along line IXxe2x80x94IX of FIG. 8, showing a part of a secondary coil. As shown in FIG. 8, the conventional high voltage transformer, which is denoted 120, has an I-shaped core 121, and an E-shaped core 123, both of which are made of silicon steel. A primary coil 125 is connected to an external power supply, (not shown) and a secondary coil 129 is connected to a magnetron (not shown). An insulating member or micasheet 127 made of a suitable insulating material is positioned between the primary and secondary coils 125 and 129, and a heater coil 131 is positioned between the insulating member 127 and the secondary coil 129. As illustrated, insulating member 127 may be formed as two separate parts.
Each of the primary and secondary coils 125 and 129 is covered with a respective insulating sheet or covering 133 for insulating the coils 125 and 129 from other components. As illustrated, the respective insulating sheets 133 can be formed of multiple parts. Beside the secondary coil 129 is installed a temperature sensor 135 for detecting temperature of the secondary coil 129 so as to protect the secondary circuit for the secondary coil 129. The temperature sensor 135 is positioned inside the insulating sheet 133 enclosing the secondary coil 129 as shown in FIG. 9. Alternately, sensor 135 can be fixed between the secondary coil 129 and the core 121 by a tape (not shown). Another insulating sheet 137 is positioned between the temperature sensor 135 and the secondary coil 129 so as to prevent the temperature sensor 135 from contacting the secondary coil 129.
In the above-described conventional high voltage transformer for a microwave oven, because the temperature sensor 135 is fixed in position by the insulating sheet 133 enclosing the secondary coil 129, the insulating sheet 133 can detach from the secondary coil 129 when the high voltage transformer 120 is in operation and the temperature of the high voltage transformer 120 can increase beyond a predetermined value. As a consequence, the temperature sensor 135 cannot be securely disposed at its optimum or desired position with respect to the secondary coil, and under conditions such as those outlined above, the temperature sensor 135 cannot precisely detect the temperature of the secondary coil. In addition, with this conventional configuration, the efficiency of insulation is not optimal. Further, because the temperature sensor 135 is fixed to the secondary coil 129 with the insulating sheet, or in the non-illustrated embodiment, to the fixing tape, the insulating sheet or the fixing tape must be removed by hand for inspecting, repairing or replacing the sensor, thereby decreasing the efficiency of any such inspection, repair or replacement.
To solve the above discussed problems, it is an object of the present invention to provide a high voltage transformer for a microwave oven in which a temperature sensor is securely positioned at its desired position relative to a secondary coil, thereby improving the detecting accuracy of the temperature sensor, and to provide a method of manufacturing such a transformer.
It is another object of the present invention to provide a high voltage transformer, and a manufacturing method therefor, wherein the associated temperature sensor can be installed and removed in a simple manner so as to permit the sensor to be easily repaired or replaced.
To accomplish these and other objects of the present invention, there is
provided a high voltage transformer for a microwave oven including a core, and primary and secondary coils, wherein the high voltage transformer further comprises an insulation molding part which encloses at least a part of said secondary coil and which includes a sensor accommodating portion, and a temperature sensor disposed or accommodated in said sensor accommodating portion for detecting temperature of the secondary coil.
Preferably, the sensor accommodating portion is formed inside of the
insulation molding part, and the temperature sensor is one of a thermostat and a thermistor. Advantageously, when a thermistor is used, a safety device such as a fuse is also employed.
In an alternative preferred embodiment, the sensor accommodating portion has the shape of a pocket, or is otherwise shaped, so that the temperature sensor can be easily put into, and taken out of, the sensor accommodating portion, and the temperature sensor comprises one of a thermostat, a thermistor and a fuse.
According to a further aspect of the present invention, there is provided a method for manufacturing a high voltage transformer for a microwave oven, the transformer including a core, primary and secondary coils, and a temperature sensor for detecting temperature of the secondary coil and the method including the steps of: accommodating the secondary coil and the temperature sensor in a molder member; molding the secondary coil and the temperature sensor accommodated in the molder member into an insulating molding part accommodating the temperature sensor, and enclosing at least part of the secondary coil such that the temperature sensor is fixed in position relative to the secondary coil.
Advantageously, the molding step comprises molding a temperature sensor accommodating portion into the molding part in which the temperature sensor is accommodated. In a beneficial implementation, the sensor and the secondary coil are molded together such that the sensor is disposed directly adjacent to the secondary coil. Advantageously, the external sensor accommodating portion is formed as a pocket defining member on an outside surface of the insulating molding part. Preferably, the temperature sensor is one of a thermostat and a thermistor.
According to another aspect of the present invention, there is provided a manufacturing method of a high voltage transformer for a microwave oven, the transformer including a core, primary and secondary coils, and a temperature sensor for detecting temperature of the secondary coil, and the method comprising the steps of: providing a molder member for forming an insulating molding part including an external sensor accommodating portion; disposing the secondary coil in the molder member; and molding the secondary coil in the molder member to form the insulating molding part with at least a part of the secondary coil molded therein and to form the external sensor accommodating portion in spaced relation to the secondary coil so as to permit placement of the temperature sensor into, and removal of the sensor from, the sensor accommodating portion. Preferably, the temperature sensor is one of a thermostat, a thermistor and a fuse.